"Donald Trump said he’d release his tax returns as soon as the president released his birth certificate, so the ball is in his court now and I know everybody is anxious to see his tax returns over the last 10 years," Gibbs told POLITICO.

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Trump first floated the trade-off in an interview with ABC earlier this month.

"Maybe I’m going to do the tax returns when Obama does his birth certificate," said the real estate mogul, whose wealth has long been a matter of dispute. "I may tie my tax returns [to the birth certificate]. I’d love to give my tax returns."

At a Wednesday morning news conference in New Hampshire following the president’s release of his birth certificate, Trump repeatedly ignored questions about whether he'd fulfill his pledge.

Asked later about Gibbs' comments, Trump told POLITICO: "Gibbs is a loser.” Maggie Haberman contributed to this report.